I also have a '58 445, and when I was restoring it a couple of years ago, I discovered the "VIN" number written in chalk on the outside of the body, on the right side footwell. It was covered by the sprayed-on undercoating that I removed to do some rust repair on the floor. Purely by coincidence, the number matches the number stamped on the aluminum plate that is screwed to the firewall on the passenger side, in the vicinity of the voltage regulator.

By the way, I had a really hard time convincing the local registry of motor vehicles that the car had only 4 digits in its "VIN" number. The clerk had to call over her supervisor to put in an override code so that the computer system would accept such a short number!

Steve